Particulate boehmite is used in the glass, catalyst and ceramic industries. Commercially, boehmite particles are prepared by digestion of aluminium trihydroxide (gibbsite, chemical formula: Al.sub.2 O.sub.3.3H.sub.2 O) in water at temperatures of 200.degree.-250.degree. C. For example, U.S. Pat. No. 3,954,957 to Koenig describes a process for the production of boehmite pigment starting from gibbsite. The process involves preliminary grinding of gibbsite to an average particle size of 1-3 microns, and digesting the ground gibbsite in the presence of a controlled amount of mineral acid at temperatures between about 180.degree.-250.degree. C. for 0.5-120 minutes. This leads to the production of a boehmite product of uniform particle size having a particle size range of between about 0.2-0.7 microns.
It is also known that when crystallized gibbsite, obtained from the well-known Bayer Process for producing alumina from bauxite, is heated to a temperature in the range of 120.degree. C. to 300.degree. C., conversion of the gibbsite to measurable amounts of boehmite occurs, particularly if the heating is rapid and coarse gibbsite particles are used. (See, for example, Oxides and Hydroxides of Aluminum Technical Paper No. 19, Alcoa Research Laboratories, 1972.) This is known as the solid state reaction since it takes place in the absence of added water. The boehmite produced by solid state reaction is embedded in a matrix of activated material. In the discussions that follow below, the term "activated" refers to the non-boehmite components of the heated gibbsite material.
It therefore is an object of the present invention to provide a method for the production of crystalline boehmite of fine particle size.
It is a further object of the present invention to provide a method for the production of boehmite with a surface area which is substantially higher than that to be expected from particles of the order of about one micron in size.
A further object of the invention is to provide a new particulate boehmite material.